Microprocessor real-time clock circuitry is controlled by a timebase enable signal that is synchronized with the bus clock signal. In a traditional bus, a timebase enable signal has a fixed relationship with the bus clock signal. Thus, a timebase enable signal is typically generated from the bus clock by removing periodically certain numbers of pulses from the bus clock. The timebase enable signal has pulses in a frequency that is proportional to the frequency of the bus clock signal; and the rising (or falling) transition edges of the pulses of the timebase signal are synchronized with the bus clock signal.
However, when a new, state-of-art bus is used, such fixed relationship may not exist. In a state-of-art bus, the frequency of the bus clock can be changed. However, the frequency of timebase enable signal cannot be changed to maintain an accurate real-time clock. Thus, the frequency relationship between the bus clock and the timebase enable signal is not fixed in such a bus.